EP0907884B1 - Process for testing the freeze-thaw resistance of solids - Google Patents

Abstract

A solid to be tested is preconditioned by drying it to a specified moisture content and its load surface is inserted downward into a test container which takes up test liquid thereby completely wetting the load surface. The test container is immersed in a temperature equalization bath which is temperature controlled. The test liquid is subjected to a predetermined temperature-time profile simulating a freeze-thaw cycle via the temperature-equalization bath. Then, at least one comparison measurement is taken to determine a change in a physical quantity representative of the inner damage to the solid. From the comparative physical values measured, the inner damage to the solid is determined based on the effects of the freeze-thaw cycle and the test liquid.

Description

The invention relates to a method for testing the Frost-thaw resistance and / or the frost-thaw salt resistance of solids. In particular, the invention is concerned with an extension and extension of the frost or freeze-thaw salt test, as described in DE OS 39 28 130 of the applicant is known.

In construction, there are materials, solids or components often exposed to special environmental pollution. Typical environmental pollution are freeze-thaw changes with and without de-icing agents. In the first case they need to be polluted Solids have increased frost-thaw resistance; in the second If there is an increased resistance to frost and de-icing salt. As before said in the original publication, the term "increased freeze-thaw resistance" without restriction to others aqueous solutions are transferred, as far as that described here Test procedure is affected.

1. die Simulation des der Umweltbelastung entsprechenden äußeren Angriffs; und

2. die Messung bzw. Bestimmung der Schädigung des Festkörpers als Folge dieses äußeren Angriffs.

The resistance test of porous solids comprises two process stages:

1. the simulation of the external attack corresponding to the environmental pollution; and

2. the measurement or determination of the damage to the solid as a result of this external attack.

a) die äußere Schädigung, insbesondere die Abwitterung; und

b) die innere Schädigung, welche mehrere physikalische Materialeigenschaften, beispielsweise die Festigkeit und Elastizität erheblich vermindert und selten von außen erkennbar ist.

When determining the damage, two types of damage can be distinguished:

a) external damage, in particular weathering; and

b) the internal damage, which considerably reduces several physical material properties, for example the strength and elasticity, and is rarely visible from the outside.

Both types of damage occur on or near exposed surfaces. The internal damage is usually on a zone in the Area of the attacked surface is limited or goes from the stress area. However, the transition is from damaged to undamaged area in the inner Flowing damage. Therefore it is extraordinary difficult, reproducible, precise criteria for the inner Specify damage that is also universal for one whole material group should apply.

The method known from the original publication is concerned deal especially with the examination of external damage or the weathering. The accuracy and reproducibility the test was thereby in the known method improved that it is ensured that the examined Test specimen with a defined content of water with or without dissolved substances - de-icing agents. To this end becomes the solid before the actual test procedure begins conditioned, especially pre-dried. Subsequently you dip the samples with the stress surface in the Solution or in water and leaves the solution or water penetrate the specimen by capillary suction. This is followed by the freeze-thaw change to simulate the Frost or the frost-de-icing salt load.

In this respect, the process according to DE-OS 39 28 130 and the extended test method according to the present invention largely agree.

The object of the present invention is a test method to make available of the type mentioned at the beginning, with its help, the internal damage to the solid or specimen with high accuracy and reproducible Results can be determined.

According to the invention, this object is achieved by a method with the features of claim 1.

This is the simulation of the load conditions particularly good that the cold and heat supply uniaxial the stress area takes place.

The internal damage to a solid body that with the described Process subjected to a freeze-thaw change was expressed as determined by research especially in the following physical sizes:

Loss of strength, irreversible change in length, waste of the static modulus of elasticity, drop of the dynamic modulus of elasticity, Change in the damping of the dynamic modulus of elasticity and change in propagation an ultrasonic signal.

At least one of these physical quantities is therefore measured in the invention. The results of measuring the entire test procedure are in accordance with the criteria of ISO 5725 reproducible and repeatable and enable a reliable quantification of internal damage.

From US-A-4283956 it is in connection with a non-generic Method known to make a solid dynamic Suspend load changes and also vibrate it to be applied at the natural frequency. This is supposed to Beginning of crack formation in the solid state can be determined.

EP-A-0448896 also describes a method for non-destructive determination of a speed of propagation body property dependent on ultrasonic waves known.

However, the invention is not based on a special measuring method limited. The selection of the measurement method used takes place according to the respective operating conditions and accuracy requirements. Known or newly developed ones can be used Measurement methods are used, the physical Size at least in the environment of the place of use or the test arrangement allow to measure.

To determine the internal damage can - without claim for completeness - the following measurement methods are used become:

A. Measurement of the decrease in strength

On non-stressed comparison bodies and on the treated ones Test specimens are the compressive strength, the bending tensile strength, the splitting tensile strength or the like Strength measured destructively. This is the procedure expensive and complex and has the disadvantage that a test specimen can only be compared once with the reference solid and finally destroyed. Monitoring the change the damage in different phases of the freeze-thaw test can not.

B. Measurement of the static modulus of elasticity

The static modulus of elasticity can be tested on a suitable test press be determined. The porous solids, especially concrete, but not only deform elastically, but also plastic. Therefore, every burden leads to an irreversible deformation. In addition, the modulus of elasticity of the concrete is not linear, so a minimum load is required is. The decrease in strength of the static modulus of elasticity as The frost resistance is directly linked to a Critical water saturation level exceeded. When the critical degree of saturation is reached, the modulus of elasticity drops after just a few freeze-thaw changes.

C. Measurement of the dynamic modulus of elasticity

The dynamic modulus of elasticity, with its real and Imaginary part, can be determined in several ways.

C.1. Measurement by natural vibration

A proven method is the measurement of the natural vibration of a given sample bar. In a suitable manner, e.g. with a hammer, a natural vibration is generated. Prefers the first fundamental is excited. It makes sense it if the hammer contains an accelerometer, so that the load is reproducibly abandoned. From the The modulus of elasticity can be calculated.

When you stimulate a test beam to vibrate naturally and store it at the same time so that it is damping-free vibrates, then you can measure alongside the natural frequency also determine the internal damping. This can be done take place that the test specimen in the nodal points e.g. on 2nd Piano pages are stored. Through suitable evaluation methods, as by recording the decaying vibrations or through a Fourier analyzer, both the natural frequency as well as the damping can be determined.

C.2 Measurement of the dynamic modulus of elasticity using ultrasound

1. Durch Anregung einer Eigenschwingung

2. durch Messung der Schallaufzeit einer Longitudinal- bzw. einer Transversalwelle.

The dynamic modulus of elasticity can be measured with ultrasound in two ways.

1. By stimulating a natural vibration

2. by measuring the sound propagation time of a longitudinal or a transverse wave.

The measurement of the sound propagation time has the great advantage that the sound can pass through the specimen both horizontally and vertically to the target. The damping can also be recorded in a direction-specific manner.

D. Measurement of irreversible thermal expansion

Internal frost damage is always irreversible thermal expansion linked. A possibility, Determining the frost damage is therefore a targeted one Measurement of thermal expansion using suitable Measurement marks.

E. Measurement of the direction of ultrasound propagation

The internal damage to a solid is usually inhomogeneous and starts from the stress area. at the method according to the invention is a stratification of the Damage parallel to the stress area is particularly pronounced. The changes according to the internal damage Speed of sound, and one at an oblique angle radiated ultrasound signal changes its direction of propagation. According to the invention, this is used to measure the inner Damage exploited.

F. Surface wave measurement

It is known to cause damage from natural stone Measure excitation of surface waves. The surface waves are generated in that the ultrasonic signal over a medium at a certain angle onto the measuring surface incident. This is the critical angle for total reflection. This will cause Ralley waves to appear on the surface of the Test specimen generated at the same angle in one Radiate the receiver.

This measurement is suitable, as the invention has recognized Has; especially for determining the damage, including the internal damage to solids within the process step e). It can be known from DE-OS 38 130 Test arrangement can be used with great advantage.

A particularly high degree of accuracy in the measurement the internal damage to a solid can be done according to the invention by a combined measuring procedure under determination the reversible change in length of the examined solid as well as using a comparative ultrasound measurement achieve if the method according to claim 5 is applied.

In a preferred development, the invention is based on the solid to be tested, preferably on the side surfaces, each measuring plates attached so that they do not weather can. The sides on opposite sides Measuring plates can include to be used the determine thermal irreversible elongation during frost attack. It is even possible to change the length to be determined at the top and bottom of the examined solid. When using flat measuring plates, an ultrasonic signal can be generated are optimally coupled into the solid, so the runtime and the damping of the ultrasound are accurate to determine. In this way, the dynamic modulus of elasticity and / or its damping direction-specific, i.e. in particular parallel and / or perpendicular to the stress surface be determined.

To uniaxial supply of cold and heat to the test Solid body and a corresponding uniaxial capillary Sucking the liquid is more preferred Further development of the invention of the solid to be tested the side surfaces sealed while the stress surface remains unsealed.

Fig. 1

eine Versuchsanordnung ähnlich derjenigen gemäß Fig. 1 der DE-OS 39 28 130, anhand der der grundsätzlich Ablauf des erfindungsgemäßen Verfahrens erläutert werden kann;

Fig. 2

ein Temperatur-Zeit-Diagramm, das einen bei der Frost-Tau-Wechsel-Belastung eines Festkörpers in der Versuchsanordnung gemäß Figur 1 typischen Temperaturzyklus veranschaulicht;

Fig. 3

ein Temperatur-Zeit-Diagramm der Frost-Tau-Wechsel-Belastung bei der Versuchsanordnung gemäß Figur 1 im Vergleich zu herkömmlichen Versuchsanordnungen bzw. Tau-Wechsel-Belastungssimulationen;

Fig. 4

eine schematische Darstellung einer Ultraschall-Meßanordnung zur Bestimmung der inneren Schädigung eines Festkörpers, der in einem für die Versuchsanordnung gemäß Figur 1 geeigneten, besonders ausgestalteten Probenbehälter angeordnet ist.

The invention is explained in more detail below on the basis of an experimental arrangement shown in the drawing. The drawing shows:

Fig. 1

an experimental arrangement similar to that according to FIG. 1 of DE-OS 39 28 130, on the basis of which the basic sequence of the method according to the invention can be explained;

Fig. 2

a temperature-time diagram illustrating a typical temperature cycle in the freeze-thaw alternating loading of a solid in the test arrangement according to FIG. 1;

Fig. 3

a temperature-time diagram of the freeze-thaw alternation load in the test arrangement according to FIG. 1 in comparison to conventional test arrangements or thaw alternation load simulations;

Fig. 4

a schematic representation of an ultrasonic measuring arrangement for determining the internal damage to a solid which is arranged in a specially designed sample container suitable for the test arrangement according to FIG.

The schematically shown as a partial view in Figure 1 Experimental arrangement is in DE-OS 39 28 130 in detail described what to avoid detailed explanations is pointed out.

The solid to be tested is placed in the experimental arrangement according to FIG. 1 to the following Conditions of use conditioned. This is done according to the preferred Embodiment of the invention in that the solids to be tested - hereinafter referred to as test specimens - is predried in a defined climate until a specified one Moisture condition is reached. The pre-drying can already take place in an associated sample container 2.

The test specimens are stored in the sample container 2 with a stress surface 1a down, so that the stress area just immersed in a test liquid 3 or is wetted by it. The position of the stress area 1a is in the embodiment shown in Figure 1 defined by elevations 4. The liquid level the test liquid 3 can be used using a level control not shown in the drawing can be set.

In the embodiment shown in Figure 1 are the side surfaces of the test specimen 1 by an essentially weatherproof coating 5 sealed. This ensures that the test liquid 3 only through bottom pores, but not through lateral solid pores can penetrate into the test specimen. The test liquid can therefore only by capillary suction from below through the Load surface 1a penetrate test specimen 1. This is essential to ensure that the test liquid the test specimen before it is subjected to alternating freeze-thaw conditions evenly up to a defined degree of saturation penetrated into the solid.

After conditioning, the test specimens are placed in the Experimental arrangement according to FIG. 1 of a defined freeze-thaw alternating load subjected. The temperature supply and removal takes place in a highly advantageous manner via a regulated Temperature bath 7 in which all sample containers 2 are immersed so far are that a good and even thermal Contact between tempering bath 7 and test liquid 3 is established is. The immersion depth of the container 2 in the temperature bath 7 can be adjusted with the help of height if necessary Mounts 8 can be varied. The cooling and heating elements of the temperature bath 7 and their control devices are not shown in Figure 1. The components are just as little for moving and circulating the bath liquid shown in Figure 1; they can be known execution his.

The temperature bath 7 is used to simulate a freeze-thaw cycle in the solid 1 a predetermined temperature-time profile exposed, such as over a period of time of 12 hours is shown in Figure 2. The temperature the temperature bath is measured at defined points, For example, centrally under the sample container 2, as in Figure 1 is illustrated by an arrow 9.

As stated above, the arrangement according to FIG a uniaxial heat supply and removal from the temperature bath 7 over the bottom surface of the sample container 2 and the stress surface 1a of the test specimen 1 reached. This heat exchange takes place due to the optimal thermal conduction with high efficiency instead, so that the regulated temperature profile 2 relatively quickly, evenly and with transfer high control accuracy to the test specimen 1 can be.

In Figure 3 are three temperature cycles with medium Spreads shown in three different test methods. It can be seen that the test methods used previously (ÖNORM and Slab Test) compared to the invention used CDF test much larger temperature-time spread have and therefore less precise and time consuming are. Basically, according to the invention method used (CDF test) during a temperature cycle conventional test methods several temperature cycles go through completely; two CDF cycles are shown in FIG.

Find the examinations of damage to the specimen by suitable measurements, preferably outside the Experimental arrangement according to Figure 1 instead. This is especially true for the determination of external damage (DE-OS 39 28 130). For this purpose, the container 2 with the test specimen 1 removed from the experimental arrangement according to FIG. 1 and sonicated in an ultrasonic bath for a predetermined time. The weathering accumulates at the bottom of the Sample container 2. The test solution is taken from the sample container decanted; the entire solid residue is dried and weighed. Determined depending on body size the weight of the solid residue obtained the degree of external damage to the test specimen.

In Figure 1, a length measuring arrangement 11 is schematic shown, with the help of the length and changes in length of the specimen 1 on opposite side surfaces can be included. The length measuring arrangement 11 is shown here in the test setup; Of course the specimen can also be removed from the container 2 and in a suitable length measuring arrangement for determining the Lengths and changes in length are used. The measurement recording can - unlike shown in Figure 1 - in several superimposed levels are made to make differences especially in the irreversible changes in length in assignment to determine different layers of the specimen can. It may also be useful to change the length of the test specimen 1 before and after the freeze-thaw alternating load in several orthogonal directions the degree of internal damage to the body more accurately and to be able to determine direction-specifically. The sealing layers 5 can also suitable plate-shaped body be the one hand the pick-up points for the length measurement define more precisely, but also as sound heads can be used for ultrasonic transit time measurements.

To determine the internal damage can also other procedures mentioned in the introduction to the description be used.

FIG. 4 shows a special and as such a new measuring method for determining the internal damage to a specimen 1 illustrates.

An ultrasound signal is from an ultrasound transmitter radiated obliquely into the stress surface 1a. Before the Freeze-thaw alternating load, the sample body 1 is undamaged, and the ultrasound signal reaches an exit point at the top of the specimen at an angle that corresponds to the Entry angle corresponds. Above the container is a Amplitude-displacement diagram shows the sound intensity at the Exit point shown ("before"). After the freeze-thaw change load the specimen is damaged. The extent of internal damage manifests itself in the degree of deflection of the ultrasound signal and thus in the geometric location of the Exit point from the specimen. Like the amplitude diagram above the sample container is the maximum value the amplitude after the freeze-thaw cycle load clearly shifted. From the distance between the two maximum values the degree of internal damage to the specimen determine relatively accurately. Serves as an ultrasound receiver the arrangement according to FIG. 4 is mounted on a carriage and parallel to the top of the specimen in the direction the double arrow 12 movable ultrasound receiver.

It is clear that various known measuring arrangements to determine the internal damage to the solid representative physical quantities can be used. By measuring the physical quantities in several different ways Directions and / or in parallel planes and / or using different measuring methods the degree of internal damage can be achieved with unprecedented Determine accuracy.

Claims (10)

1. A method for testing the freeze-thaw resistance and/or freeze-thaw and de-icing agent resistance of solid bodies wherein:

   a) the test specimen is conditioned, e.g. is pre-dried, by adjusting a defined moisture condition to the ensuing conditions of use;

   b) the conditioned solid body, with a surface of exposure faced to the bottom, is placed into a specimen container for a test medium in such a manner that the surface of exposure is in close contact with the test medium;

   c) a contact between the solid body and the test medium is maintained long enough to reach a defined degree of saturation of the solid body; and

   d) the test medium above a coolant bath is subjected to a predetermined temperature-time profile to simulate a continuous freeze-thaw cycle in the solid body;
      characterized in that
      during the method steps b) through d), the test specimen is held in the specimen container in such a manner that moisture as well as heat are transported uniaxially, and substantially perpendicular to the surface of exposure, into the body; and

   e) at least one reference measurement is carried out to determine the change of a physical quantity of a solid body before and after the method steps b) through d) wherein at least one of the following changes in physical quantities is determined:

   decrease in strength;

   irreversible change in length;

   decrease in static modulus of elasticity;

   decrease in dynamic modulus of elasticity;

   change in damping of the dynamic modulus of elasticity;

   change of the direction of propagation of an ultrasonic signal,

   whereby the internal damage of the solid body owing to the preceding attack by freeze-thaw cycles and the test medium is determined.
2. The method according to claim 1, characterized in that said solid body is thrown into the natural vibrations and that from said vibrations the dynamic modulus of elasticity and/or its damping are/is determined.
3. The method according to claim 1, characterized in that ultrasonic waves are coupled into the solid body and their transit time is measured and that the dynamic modulus of elasticity and/or its damping is/are determined out of ultrasonic transit time.
4. A method for testing the freeze-thaw resistance and/or the freeze-thaw and de-icing agent resistance of solid bodies according to any of claims 1 to 3, characterized in that the solid body in contact with a test medium is subjected to a freeze-thaw cycle, and that the solid body, before and after freeze-thaw cycles, is subjected to a comparative length measurement to determine the irreversible change in length of the solid body as well as a comparative ultrasonic measurement, wherein measuring plates are mounted on two opposed surfaces of the solid body, especially on two lateral faces, in such a manner that they are not able to undergo scaling and that the change in the dynamic modulus of elasticity and/or its damping are/is determined from the comparative ultrasonic measurement.
5. A method according to any of claims 1 to 4, characterized in that the test specimen is sealed in such a manner that the test medium cannot penetrate into the sides of the specimen whilst the surface of exposure remains unsealed.
6. A method according to any of claims 1 to 5, characterized in that the dynamic modulus of elasticity and/or its damping is determined in a specific direction, i.e. in particular parallel or perpendicular to the surface of exposure, and this in such a way that the ultrasonic signal passes the tested body in a given direction and that the ultrasonic transit time is determined specifically direction-dependent.
7. A method according to any of claims 1 to 6, characterized in that the irreversible length change is determined in dependence on direction, i.e. in particular parallel and/or perpendicular to surface of exposure.
8. A method according to any of claims 1 to 7, characterized by the use of a test liquid, which wets the surface of exposure of the solid body, as test medium.
9. A method according to any of claims 1 to 7, characterized in that the test medium contains a porous storage medium and test liquid stored in it.
10. A method according to any of claims 1 to 9, characterized in that the internal damage of the solid body is determined by the measurement of the change in direction of propagation of an ultrasonic signal in the solid body.

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